The present method relates to plants for sorting items of the type used wherever it is necessary to deal with a remarkable amount of items, as, for instance, in post offices, in mail order companies and the like.
It is a method in which the different functions are controlled by a central computer which synchronizes the various functions and controls the course of the operations.
A plant of this type includes a fixed path along which runs a plurality of carriages or units, on which the items to be sorted are laid; these are unloaded automatically when the relevant carriage passes in correspondence of a collecting area determined when the item is introduced in the apparatus, by means of computer controlled and actuated devices.
Plants of this type are illustrated in the following Italian patents and/or patent applications in the name of the same applicant: patents Nos. 1,151,648, 1,152,067, utility model No. 180,771, applications Nos. 22476 A/83, 21310 B/85, 24227 B/85, 25859 A/81, 21774 B/82, 23110 A/84, 22264 A/84 and 20779 A/85. Each item to be sorted is coded by an operator and placed on the sorting circuit in induction stations the number of which varies according to the expected sorting flow.
Along said circuit, which may develop according to different shapes and sizes, there runs a train of units occupying the whole path or a part of it.
The units are set in motion, according to methods well-known in the art, e.g. by means of a continuous driving chain (solution adopted when the path is substantially a rectilinear one) or by means of electric motors located on board of the units and fed by power bars parallel to the path (solution preferred when the path is a carrousel).
The items, conveyed by the units, reach the collecting stations where they are unloaded. The unloading of the items is carried out by means of mobile belt conveyors forming the load surface of the units. Therefore, when an item is to be unloaded, the belt conveyor of the unit is driven sending tension to the relevant motor by means of bus bars (different from the power bars and sectioned in correspondence with the unloading stations) so as to allow drive control of the only unit-belt conveyor involved in the unloading. The unloading may be carried out at both sides of the sorting path simply by inverting the sense of rotation the belt conveyor, the direction of rotation of which is perpendicular to the unit motion. The object of the present invention is to increase precision and reliability of such sorting plants, intervening so as to assure a correct positioning of the item on the conveyance plane.